IODINE. 383 



hydrobromic and phosphoric acids, which proves it to be P Br 5 ; 

 and the latter affords hydrochloric and phosphorous acids, 

 which proves it to be P Br 3 . The liquid bromide does not 

 freeze at 5, and like the liquid chloride of phosphorus is capa- 

 ble of dissolving a large quantity of phosphorus. 



Bromide of carbon. It is probable that the compound des- 

 cribed as such by Serullas is bromoform, C 2 H Br 3 .* 



Bromide of silicon Is prepared by a similar process as the 

 chloride of silicon. It is a liquid boiling at 302 and freezing 

 at 10. By water it is resolved into hydrobromic acid and 

 silica. 



SECTION XII. 



IODINE. 

 Eg. 1579.5 or 126.57; I; densltij 8707-7; fTi- 



Iodine was discovered in 1811, by M. Courtois of Paris, in 

 kelp, a substance from which he prepared carbonate of soda. 

 Its chemical properties were examined by Clement, and after- 

 wards, more completely by Davy and Gay-Lussac, particularly 

 the latter.f A trace of iodine has been observed in sea-water 

 (Schweitzer), but it is more abundant in the fuci, ulvi and other 

 marine plants, and also in sponge, the ashes of which contain 

 iodide of sodium. It is known also to exist in one mineral, a 

 silver ore of Albaradon in Mexico. Iodine has not as yet, I 

 believe, found any important application in the useful arts, but 

 it has proved a valuable addition to the materia medica. 



Preparation. The greater part of the iodine of commerce is 

 prepared at Glasgow from the kelp of the west coast of Ireland, 

 and western islands of Scotland. The sea-weed thrown upon 

 the beach is collected, dried, and afterwards burned in a shallow 

 pit, in which the ashes accumulate and melt by the heat, being 

 of a fusible material. The fused mass broken into lumps forms 

 kelp, which was prepared and chiefly valued at one time for 

 the carbonate of soda it contains, which varies in quantity from 

 2 to 5 per cent. It is not all equally rich in iodine. According 

 to the observation of Mr. Whitelaw, the long elastic stems of 

 the fucus palmatus afford most of the iodine contained in kelp, 



* An. de Ch. et de Ph. t. 39, p. 225. 



t Davy in Philosophical Transactions for 1814 and 1815 ; Gay-Lussac in the 

 Annales de Chimie, t. 88, 90 and 91. 



